It is known in the overhead crane art to which the present invention particularly appertains to construct the runway rails and bridge girders of steel, with attendant cost, weight and operational disadvantages. More specifically, and notwithstanding foreign competition, steel of the structural type commands what some regard as premium prices. Related thereto is the fact that many products requiring transport by overhead cranes during the manufacture thereof are presently of relatively lesser weight, exemplified in the automotive industry by the substitution of aluminum or plastics for steel. Cost and weight penalties accordingly characterize the utilization by the prior art of steel for runway rails and bridge girders or transfer beams.
It is also known that in the overhead crane art that the runway rails and bridge girders present in cross-section what are termed flange flat track or "I" beam configurations. In some environments this creates the problem of deleterious substances such as rust or foreign objects coming in contact with the trolley and related mechanisms. It has accordingly been proposed to utilize track sections of channel-like configuration formed of confronting half-sections of steel welded at their junctures. Again, the earlier noted cost and weight disadvantages subsist.
It is further the current practice in the crane art to employ trolleys wheels constructed of steel which travel upon steel runway rails and steel bridge girders. This presents a relatively high intensity sound level, which when combined with other noises common to a production line operation, may produce a decible rating approaching the average pain level.